Field of the Invention
The invention relates to a method and a device for detecting a preinjection in an internal combustion engine operating with a direct injection.
Internal combustion engines using a direct fuel injection have a considerable potential for reducing the fuel consumption combined with a relatively low pollutant emission. Unlike with a manifold fuel injection, with a direct fuel injection, fuel is injected directly into the combustion chamber at a high pressure.
Injection systems with a central pressure accumulator (common-rail) are known for this purpose. In such common-rail systems, a high-pressure pump is used to build up in the common rail a fuel pressure, which is controlled by an electronic controller of the internal combustion engine via a pressure sensor and a pressure controller and which is available substantially independently of the engine speed and injection quantity. The fuel is injected into the combustion chamber via an injector having a solenoid valve or a piezoelectric valve. The injector receives its signals from the controller. Owing to the functional separation of pressure production and injection, the injection pressure can be selected substantially independently of a current operating point of the internal combustion engine.
The combustion noise of an internal combustion engine operating with direct injection, in particular the noise of a diesel internal combustion engine, can be substantially reduced when the calculated fuel quantity is not injected at once, but is distributed over two injection processes per cylinder stroke. In this case, a quantity of fuel, which is small compared to the total quantity to be injected and is also known as a pilot quantity, is injected during a preinjection process, and the main quantity is injected after a period which depends, as a rule, on the operating point of the interna combustion engine and is expressed in degrees of crank angle (see for example Published German Patent Application DE 39 35 937 A1). A reduction in the pressure gradient in the combustion chamber is thereby achieved, as a result of which the noise behavior of the combustion and thus of the internal combustion engine is substantially improved.
Without a preinjection, not only the noise behavior of the internal combustion engine is worse, but also the exhaust emissions increase.